Stretch-testing machine



Jan. 17, 1926.

, 1,656,246 R. P. STEVENSON STRETCH TESTING MACHINE Filed. Au. 9. 1926 IN VEN TOR.

A TTORNEYS.

Patented Jan. 17, 1928.

UNITED STATES PATENT. OFFICE.

ROBERT P. STEVENSON, PROVIDENCE, RHODE' ISLAND, ASSIGNOK'TO am! L.

5001"]! COMPANY, 01! PROVIDENCE, RHODE ISLAND.

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STRETCH-TESTING mom...

Application filed Au ust a, me. Serial Ho. 120,210.

This invention relates to an improved machine for testing elongatable mater al such as rubber or the like; and has for its object to rovide means for passing an elecl tric s ar through a specially prepared chart rom the back to the front thereof at predetermined intervals as the pointer terminal of the spark gap is moved along. its rear surface .to indicate on its-front s1de as the stress strain is applied to the sample being tested whereby the chart may be removed from the machine and these points roject to corresponding percentage lines on its front face anda curve drawn through the plotted points,-which curve represents the behavior of the sample elongatedwithout further mathematical calculations.

A further object of the-invent on is to provide means for varying the resistance to lo the pull on the upper work grlpping aw.

With these and other objects in view, the invention consists of certain novel features of construction, as will be more fully described, and particularly pointed out in the 1 ap ended claims.

n the accompanying drawings:

Figure 1 is a diagrammatic view illustrating a sample being tested and the compeneating weight as connected to and nsulated from thespark point; also representing an electric circuit "adapted to be closed by a foot operated switch.

Figure 2's an edge ShOWIDg a platen with a chart mounted as thereon and the spark point as mounted on a guide bar to be moved horizontally along the surface of the chart, the point being connected to and insulated from the-compensating weight. Figure 3'is a perspective view of one of the removable compensating weights adaptedto be applied to t e weight arm. :37 Figure 4 is a view. showing a (general shape of sample of rubber to be teste a as ced to the front when the chart is applied to the supporting platen.

igure 6 shows the ruling on the front face of the chart. and also shows the indi- 0 eating oints which were pierced from the back of the while in position on its 5 shows the rear face of the chart platen and. the curves plotted from these points on the front b .projecting these points across to the di erent vertical lines on the face of the chart.

Rubber samples are tested to obtain their tensile strength per square inch and the standard samples have a middle portion onequarter inch in width by one-tenth of an inch in thickness and the standard way of charting a curve to indicatethe behavior of the sample tested is so as to read from the left to right on the chart and inorder,

to produce such a reading on a standard rubber testing machine, I have arranged a s ecially ruledchart which consists esseninch. The sheet is provided with an unruled space at the left. The reverse side or rear face of this sheet has a line across one side coinciding with the zero poundage line on the front and the rear face is ruled at rightangles to the zero line at a portion c'oinc1din 'view partly in section.

with the unruled portion on the front. ruled portion on-the rear faceis numbered consecutively to designate the different samples tested. The c rator now places the chart on a sparking p aten which forms one terminal of the spark gap of the machine with the reverse side or rear face outwardly, he then positions the spark point or other terminal of the spark gap on the vertical zero line and starts the machine. At each 100 percent of elongation or stretch of the sample and at the break he closes the circuit b a' foot switch and causes an electric spar of high tensionto pass from the ppinter through the paper to the platen hind it. After this has been accomp ished and one or more tests has been made, the chart is removed and reversed side for side, and the punctured points are projected to the corresponding vertical percentage lines usually of dumb-bell shape, one end bein connected to the clamp 11, its opposite en to the clamp 12. The clamp 111s supported on the head 13 which is pivotally mounted on K the shaft 14. To this head is connected a depending weight arm 15 carrying a weight 16 On this shaft 14 is mounted the segments 17 meshing with a pinion 18 to move the pointer 19 over the face of the graduated dial 20 to indicate in pounds .or other unit of measure the 'pull being exerted during the testing operation.

The weight arm is provided wlth a ratchet pawl '21 in engagement with the rack 22 to prevent the arm from returning after the sample has been ru tured.

Power is herein s own as being applied to the lower end of the sample throug a rack 23 and pinion 24.

Anelectrical conducting platen 25 is su ported adjacent the weight arm on which t e chart 26 is supported by the clamps 27. The platen is movable verticall in the guides 28. On these guides and insu ated therefrom is supported a guide rod 29 on which is slidably mounted aspark pointer 30 and this pointer has a bearing 31 which is connected to the wei ht 16 through the rod 32 which is insulate therefrom by the member 33.

In order to provide a high tension electric circuit, I have connected a wire 34 to the end of this. guide rod 29 which is connected through a coil 35, wire 36 to the battery 37 and switch 38 back throu h wire 39 to the laten guide frame 28 w ereby when this cot switch is operated it closes the circuit and causes the spark to jump from the int 30 through the chart 26 to the platen on which it is supported.

The high tension spark is of suflicient force to puncture the chart so that these points of puncture may be readil discernable on the opposite side or front ace of the chart.

The standard sample 10 of rubber is preferably formed of dumb-bell sha e, .as illustrated in Figure 4, having a mi dle reduced portion having marks as at 39 to represent an inch of space therein on its surface. This sample is then connected between the upper and lower clamps 11 and 12.

Before the test this sample is carefully drawn through its calibrated and if it is of the standard size of one-quarter inch in width by exactly onetenth inch in thickness the standard weight 13 on the weight arm 15 is emplo ed, but if the thickness should be greater t an standard, a greater weight is employed for the arm, for instance, one pound of weight is added for each 1/5000 variation in the thickness of the sample, so that if the sample is a the upper portion thereof and the downwardly yielding movement of the upper clamp jaw, while the lower trammel point 43 is moved downwardly over the scale following the lower mark 39 to indicate the stretch of the sample.

At each percent elongation of the sample is indicated by these trammel points, the operator presses the foot switch 38 and closes the circuit, thus causing the spark to jump through the paper and puncture the chart at these different intervals of stretch and also again at the point of breaking. After this sample has been broken the mechanism is returned to starting position, another sample is positioned between the clamps 11 and 12, the pointer is automatically moved back to its starting position Hip when the weight 16 is released to swing back to zero, the platen with upwardl describer is repeated and which operation is repeated with each sample teste After thetest is completed the chart is removed from'the platen, turned over with its front side outward then the different oints in each row of punctures are proected progressively across to the corres 0ndmg percentage line on the chart an curve for each of the different samples is plotted points, which curve represents the pounds pull per square inch of each one hundred percent elongationsof the sample, which result is accurately obtained without further mathematical calculations thus saving much time and eliminating mistakes that might occur in making such calculations.

The foregoing description is directed soleits chart is moved .ly towards the construction illustrated, but

I desire it to be understood that I reserve the privilege of resorting to all the mechanical changes to which the device is susceptible,

one line, and the operation above 7 the s the invention being defined and limited only y the terms of the appended claims,

I- claim: 1. In a rubber testing machine, means for stretching the rubber sample, means for 'measuring the tension on the sample, a

means for manually controlling the electric circuit'to cause a spark to jump said gap and pierce said chart at any predetermmed point of stretch of said sample.

2. Ina rubber tester, means for progressively applying a testing strain to a rubber sample, means for measuring the elongations, means for measuring the pounds ull on the sam le in combinationwith a c art carrying p aten, a chart on the platen, an

electric circuit,.a sparking oint in said circuit means .formoving' sai point along the surface of the chart and means for closing the circuit, at predetermined intervals to cause a .spark to jum from said point through the chart to in 'cate on the reverse moved along the side as the point is moved along its surface.

3. In a rubber tester, means for pro essively applying a testing strain to a ru ber sam 1e, means for measuring the ounds pull on t e sample, in combination with a chartcarrying platen, a chart on the platen, an electric circuit, a sparking oint in said circuit means for moving sai point along the surface of the chart and means bywhicl'i the circuit may be closed at predetermined intervals to cause a' ark to 'ump from said point through the art to indicate on the reverse side thereof as the point is moved ,the circuit at desire along its surface, and means for varying the to resistanceto the pull on the upper work gripping aw. a 4. In a rubber tester, means for pro essively applying a testing strain to a rui ber sample or measuring the elongation of the 5 sample, means including a com ensating weight arm and a graduated dial or measuring the pounds pull on the sample,a chartcarrying platen, an electric circuit, an' insulated sparking Point mounted to be moved along the face'o the chart mounted on the platen, an insulated connector between'said point and weight arm for advancing said point, and a switch for closing the circuit at desired intervals to cause a spark to jump and burn throughthe chart supported on the platen.

5. ha rubber tester, means for progressively applying a testing strain to a ru ber sample, means for measuring the elongation 00 of the sample, means including a compensation weight arm and a raduated dial for measuring the poundsp l on the sample, a chart-carrying laten, an electric circuit, an insulated spar 'nfg' point mounted to be 06 ace of the chart mounted on the platen, an insulated connection between said point and weight arm throu h which said point is advanced, a switch or advancing said point a switch for closing intervals-to cause a spark to jump through and pierce the chart carried by the platen, and means whereby the weight of'said compensating arm may be varied to compensate for the pull on test samples of difierent areas.

In testimony whereof I afiix my signature.

ROBERT P. STEVENSON. 

